The bragging rights were up for grabs and it was Buehrle who came through by tossing 6 1/3 quality innings to lead the Blue Jays to a 4-3 victory in front of 15,755 fans at Rogers Centre.
"I tried not to take a look at too many guys stepping into the batter's box because I knew I would start laughing or something bad would happen," a relieved Buehrle said after earning his first win with the Blue Jays. "I just tried to focus on the glove, which is not me, I'm usually out looking around and having fun.
"It was different seeing the Sox uniform in the batter's box, usually it's behind me. It's weird rooting against those guys. I rooted for them for 13 years and wanted them to win every game. This is the first game in I don't know how long that I'm actually rooting against them."
Buehrle has now faced all 30 teams in the Major Leagues and the only team he has yet to beat is the Mets. All but 14 of his 175 career wins came while wearing a White Sox uniform, so it's easy to understand why there might have been a sense of uneasiness before his start.
The 34-year-old established himself as one of the more reliable pitchers in baseball while on Chicago's South Side. He made four All-Star teams and played a pivotal role in helping lead the club to a World Series championship in 2005.
But Buehrle's friends became foes for at least one night, though, as he found himself in the awkward position of competing against those who went to battle for him so many times in the past.
"I think walking in, I don't want to say nerves, I think it was just not knowing what to expect or what to do, just looking over there and seeing all of those guys," Buehrle said. "I think once I get on the field, I'm nervous before every game, but once I get on the field and start throwing, the nerves kind of leave. It was just weird seeing them on the other side."
Buehrle won't admit it but the unique feeling could have played a role early in Monday's game as he struggled to find a groove. Two of the first three batters reached base before Paul Konerko singled home the first run of the game.
Another run came around to score later in the first on a single by Dayan Viciedo, but Buehrle was able to settle in from that point on. He allowed just one more runner to reach scoring position until he was taken out in the top of the seventh inning.
The most pivotal moment came in the fifth inning with runners on the corners and two outs. Konerko once again was at the plate, but this time he came out on the losing end.
"It felt a little weird and it's not really something you want to have to deal with, for me anyway, just because I played with him for so long," said Konerko, who struck out. "I don't think I had much fun with it and I don't think he did, either. But it was a good ballgame, he pitched well."
Buehrle was charged with just the two runs on nine hits and two walks. He struck out three while throwing 59 of his 102 pitches for strikes. The outing was a noticeable improvement on his first two starts, which saw Buehrle allow 11 earned runs in just 9 2/3 innings.
The results will be viewed as a step in the right direction but, as always, Buehrle remained even-keeled. He didn't get too low after surrendering six runs to the Tigers in the cold, wet conditions at Comerica Park and he's not about to get too high after his first win.
"I'm the same pitcher no matter what team, no matter what batters are in there," Buehrle said. "Just try to hit my spots, keep the ball down.
"My cutter was working a little bit better than it has. ... Just seemed like everything was working. J.P. [Arencibia] called a great game, we had a good game plan going in. Obviously knowing that they know me, it kind of changes a few things up."
Even though the Blue Jays fell behind by two early on, it didn't take long to get those runs back. Emilio Bonifacio led off the first with a double and later scored on a sacrifice fly, and Arencibia followed with a solo shot to right-center field for his fourth homer.
Maicer Izturis added another solo shot off White Sox starter Gavin Floyd in the bottom of the second. Izturis' shot to right came on a 1-1 pitch and marked his second of the season despite his reputation as being a soft-hitting infielder.
Recent Blue Jays callup Munenori Kawasaki also got into the action in the fourth when he sent a one-out triple to the gap in left-center field. He came around to score later in the frame as Floyd was charged with four runs on nine hits while striking out six.
There was enough offense to get the job done but in the end, it all came back to pitching.
"[J.A.] Happ was really the only one that was consistent early on, but they have too good of a track record, that was going to change," said manager John Gibbons, whose team now has three consecutive quality starts after early struggles. "They're like anybody else, even as successful as they've been, they need good outings for confidence, too.
"They don't start to worry, they don't start to panic, but they need good outings. ... They're all good pitchers and that's definitely one of our strengths."